This application is based on and claims priority to Japanese Patent Application No. 11-147271, filed May 26, 1999, the entire contents of which is hereby expressly incorporated reference.
1. Field of the Invention
The present invention relates to an engine sensor and a feedback-control system for an engine. More specifically, the present invention relates to an improved engine sensor assembly used for a feedback-control system of an outboard motor engine.
2. Description of Related Art
In all fields of engine design, there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued high or higher power output. In pursuit of better fuel economy and emission control, various types of control systems have been developed in conjunction with internal combustion engines. One of the more effective types of controls is so-called xe2x80x9cfeedbackxe2x80x9d control. With this type of control, a basic air/fuel ratio is set for the engine. Adjustments are then made from the basic setting based upon the output of a sensor that senses the air/fuel ratio in the combustion chamber in order to bring the air/fuel ratio into the desired range.
Normally, the type of sensor employed for such feedback-control is an oxygen (O2) sensor which outputs an electrical signal. Generally, when the output signal voltage is high, little oxygen is present in the exhaust, indicating that a combusted air/fuel charge was rich in fuel. On the other hand, when the output signal voltage is low, substantial amounts of oxygen are present in the exhaust, thus indicating that a combusted charge was rich in air.
A conventional oxygen sensor is normally associated with a wave forming circuit which manipulates the output of the sensor to indicate an xe2x80x9cOnxe2x80x9d signal when the voltage of the output signal exceeds a reference voltage (i.e., a signal which results when the supplied charge is rich in fuel). On the other hand, the circuit manipulates the signal to indicate that the sensor is xe2x80x9coffxe2x80x9d when the voltage of the output signal does not exceed the reference voltage (i.e., a signal which results from a supplied charge is rich in air).
The control operates on a feedback-control principle, continuously making corrections to accommodate deviations from the desired air/fuel ratio. Adjustments are made in stepped intervals until the sensor output goes to the opposite sense from its previous signal. For example, if the mixture is too rich in fuel (i.e., the sensor signal is xe2x80x9conxe2x80x9d), then lean adjustments are made until the mixture strength is sensed to be lean (i.e., the sensor signal turns xe2x80x9coffxe2x80x9d). Adjustments are then made back into the rich direction in order to approximately maintain the desired ratio.
Most commonly, the oxygen sensor is the type which utilizes inner and outer platinum or platinum coated electrodes. However, the platinum acts as a catalyst, which catalyzes exhaust. For example, oxygen remaining in the exhaust may be catalyzed with carbon monoxide at the platinum electrode interface, creating carbon dioxide. When the effects of the platinum in improving exhaust gas emissions may be advantageous, the oxygen content of the gas being sensed can be affected to a degree which causes the sensor to provide inaccurate data, causing the control to adjust the air/fuel ratio erroneously.
For example, while the actual oxygen content of the exhaust system may correspond to an air rich air/fuel charge such that the actual signal from the sensor should indicate that the sensor is xe2x80x9coffxe2x80x9d the above-described effect may cause the sensor to indicate little oxygen is present (i.e., as if a rich fuel charge has been supplied) by an xe2x80x9conxe2x80x9d signal. In that instance, the feedback-control is arranged to adjust the air/fuel ratio in the fuel rich direction in response to the xe2x80x9conxe2x80x9d signal even though the mixture is already fuel rich.
A known mounting arrangement for an oxygen sensor is illustrated in FIG. 1. As shown in FIG. 1, an oxygen sensor assembly 10 includes an oxygen sensor 12, an oxygen sensor housing 14, and a sleeve 16.
The housing assembly 14 includes a sensor chamber 18 defined in a housing body 20. A sensor element 22 of the oxygen sensor 12 is disposed within the sensor chamber 20. The sensor chamber 18 tapers radially inwardly towards a lower end thereof and communicates with a gas guide 24 via a communication passage 26. The housing body 20 is connected to an engine block 28 and communicates with a cylinder bore 30 defined in the cylinder block 28 via a throughole 32 which extends between the cylinder bore 30 and an outer surface of the engine body 28.
The sleeve 16 is disposed within the throughole 32. Additionally, the sleeve 16 includes an inner flange 34 disposed on an inner end of the sleeve, i.e., proximate to the cylinder bore 30 and an outer flange 36 disposed at a distal end of the sleeve 16, i.e., distal from the cylinder bore 30.
As shown in FIG. 1, the inner and outer flanges 34, 36 are relatively thick. Additionally, the inner flange 36 contacts both the engine body 28 and the housing body 20. Between the flanges 34, 36, and annular air gap 38 is formed between an outer surface of the sleeve 16 and an inner surface of the throughole 32.
One aspect of the present invention includes the realization that known engine sensing assemblies, such as oxygen sensor assemblies, have proven to be inadequate. In particular, it has been found that known combustion condition sensors do not satisfactorily maintain the temperature of combustion products for sensing purposes. For example, it has been found that sleeves, such as the sleeve 16 illustrated in FIG. 1, allow an excess amount of heat, under some operating conditions, to escape from the combustion gases flowing through the throughole 32, thus lowering the temperature of the gases sufficiently to prevent the reliable operation of the oxygen sensor. It has been found that the escaping heat is transferred into the housing body 20 of the sensor assembly 14 via one of the sleeve flanges.
As shown in FIG. 1, the inner flange 36 has a substantial thickness and contacts both the inner surface of the throughole 32 formed in the engine body 28 and the inner surface of the guide passage 24 formed in the housing body 20. Thus, heat from the. combustion gases flowing through the sleeve 16 can be transferred into the housing body. 20 via the inner flange 36, thus cooling the sleeve 16. Additionally, heat can also be transferred between the engine body 28 and the housing body 20, because the flange 36 contacts both the engine body 28 and the housing body 20. It has been found that by constructing the sleeve 16 so as to have only two thick flanges 34, 36 at its proximate and distal ends, such that the outer flange 36 contacts both the throughole 32 formed in the engine body 28 and the guide passage 24 formed in the housing body 20, the sleeve 16 is excessively cooled, thereby allowing deposits to enter the guide passage 24 and damage the sensor element 22. Thus, it is desireable to provide a sleeve that better maintains the temperature of combustion gases flowing therethrough.
Heat stored in the sleeve 16 is also useful for burning deposits that may enter the sleeve 16, thus preventing such deposits from adhering to the sensor element 22 of the oxygen sensor 12. It has been found that by constructing the sleeve 16 so as to have only two thick flanges 34, 36 at its proximate and distal ends, such that the outer flange 36 overlaps both the throughole 32 formed in the engine body 28 and the guide passage 24 formed in the housing body 20, the sleeve 16 is excessively cooled, thereby allowing deposits to enter the guide passage 24 and damage the sensor element 22.
As noted above, direct injected engines are becoming more popular. In a direct injected engine, lubricant is delivered directly to the crankcase without being mixed with fuel. Thus, droplets of lubricant entering the combustion chamber are more viscous in direct injected engine as compared to engines which mix lubricant with fuel before injection. It has been found that such direct injected engines can suffer more frequent oxygen sensor failure due to the higher viscosity lubricant droplets that reach the oxygen sensor 12. Thus, it is advantageous to construct an engine sensor assembly such that the sleeve disposed in the throughole formed in the cylinder wall more reliably bums deposits, such as oily deposits, during operation of the engine, thereby preventing such deposits from reaching the engine sensor.
According to another aspect of the invention, a sensor assembly for an internal combustion engine comprises a sensor chamber, a sensor body having a sensor element disposed in the sensor chamber and a first passage connecting the combustion chamber of the engine with a sensor chamber. A sleeve extends through the first passage. The sleeve includes at least three flanges supporting the sleeve within the first passage so as to define a gap between an inner surface of the first passage and outer surface of the sleeve. By constructing the sleeve with at least three flanges, the thickness of each sleeve can be reduced as compared to the thickness required for sleeves having only two flanges. Thus, the heat transferred from the sleeve to the sensor housing can be reduced. Preferably, two of the three flanges are supported within a throughole defined in the engine body and only one flange is supported by the sensor housing. As noted above, by using three flanges, the flanges can be made thinner than the thickness required for sleeves having only two flanges. Additionally, by constructing the sleeve such that only one flange is supported by the sensor housing, there is less surface area contact between the sleeve and the sensor housing, thus further limiting transfer of heat from the sleeve to the sensor housing.
Another aspect of the invention includes the realization that thermal insulation provided by the sleeve is further enhanced if the inner diameter of the sleeve extending through the first passage is at least one-half as large as the outer diameter of the sleeve.
Thus, according to a further aspect of the invention, a sensor assembly for an internal combustion engine comprises a sensor chamber, a sensor body having a sensor element disposed in the sensor chamber, a first passage connecting the combustion chamber with a sensor chamber, and a sleeve extending at least partially through the first passage. An inner diameter of the sleeve is at least one-half as large as the outer diameter of the sleeve.
Another aspect of the invention includes the realization that the various passages and/or chambers which allow combustion gases to reach a combustion condition sensor of an internal combustion engine can be configured to define a resonance chamber. Depending on the relative sizes of the passages, chambers, and the corresponding combustion chamber, this resonance chamber can be tuned such that resonance frequency of the chamber is achieved at a frequency that corresponds to an engine speed that is within the normal range of operating speeds of the engine. However, it has been found that at resonance, a combustion condition sensor such as an oxygen sensor, can be damaged from overheating.
For example, at resonance, the relative movement between the combustion gases and the sleeve can increase significantly thereby increasing the rate of thermal conduction from the gases into the sleeve as well as the oxygen sensor. As the temperature of the sleeve rises, the temperature of the sensor chamber also rises, thus raising the temperature of the sensor itself and increasing the chance of damage to the sensor.
Thus, according to another aspect of the invention, a sensor assembly for an internal combustion engine includes a sensor and a housing defining a resonance chamber. The housing is configured to receive the sensor such that the sensor is exposed to the resonance chamber. In the present sensor assembly, the resonance chamber is configured such that a resonance frequency of the resonance chamber is not less than approximately the maximum rated speed of the engine. Thus, the sensor assembly is less likely to be subjected to significant resonance of the combustion gases during operation of the engine.
Yet another aspect of the invention includes the discovery that during certain states of engine operation, the output of certain combustion condition sensors does not reliably correspond to the actual combustion condition. For example, it has been found that when a throttle valve is opened greater than 50%, the flow of air into the combustion chamber, and thus a corresponding oxygen sensor communicating with the combustion chamber, is sufficiently large to cause the sensor to erroneously indicate that a lean mixture has been combusted. Such an erroneous lean mixture indication causes the engine controller to compensate by increasing the amount of fuel injected, thus wasting fuel. Similarly, at engine speeds above approximately 3000 rpm, the speed of induction air flowing into the cylinder and thus the sensor chamber, can also cause an oxygen sensor to erroneously indicate a lean mixture.
Accordingly, an internal combustion engine according to another aspect of the invention, comprises an engine body defining at least one combustion chamber and a charge former configured to deliver fuel charges to the engine body for combustion in the combustion chamber. A combustion condition sensor communicates with the combustion chamber. A controller controls the operation of the charge former in response to an output of the combustion condition sensor when the engine is in a first operational state. However, when the engine is in a second operation state, the controller controls the operation of the charge former irrespective of the output of the combustion condition sensor.
By including a controller which utilizes the combustion condition sensor output in one operational state for charge forming control but not during another operational state, the present internal combustion engine can more effectively prevent erroneous information from affecting the calculations performed for controlling the air/fuel ratio of the charge delivered to the engine body.
Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments which follow.